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On her daily walk to the scientific station, biologist the researcher stoops near a shallow pond surrounded by thick vegetation and retrieves a small green audio recorder.

The device was left there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, known by local scientists as an non-native species with consequences that scientists are just beginning to understand.

Although abounding with remarkable animals – such as ancient giant tortoises, swimming lizards, and the well-known birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago off the coast of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this shifted. Several tiny amphibians made their way from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

Genetic studies indicate that, over the years, there have been multiple accidental introductions to the archipelago, and the frogs now have a firm foothold on two locations: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been finding it difficult to monitor, calculating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the protected natural reserve.

When San José tagged amphibians and attempted to find them in the subsequent week and a half, she could locate just one marked frog occasionally, indicating their populations were massive.

They estimated 6,000 frogs in a single pond. "Our estimates are still very low," says the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic chaos they cause. "The amount of frogs and the noise – it's truly incredible," comments the scientist.

For the researchers, their nocturnal mating calls are helpful in determining their presence in far-flung areas, using audio devices like the one near San José's workplace.

But local agricultural workers say the calls are so loud they prevent sleep at night.

"During the rainy period, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"Initially it was a shock, observing the first frogs in the area," says the farmer, who started observing their abundance about three years ago when one leaped on her palm as she was walking out of her house.

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for almost three decades, scientists still know very little about its impact on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very common for invasive organisms to prosper, as they have none of their enemies. The islands has over sixteen hundred introduced types, many of which are significantly affecting the safety of its endemic ones.

A 2020 research indicates the invasive frogs are hungry insect consumers, and might be unevenly consuming uncommon insects found only on the islands, or reducing the food sources of the region's rare avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have shown some unusual characteristics, including surviving in brackish water, which is uncommon for frogs.

Their development process is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: San José observed one which remained as a larva in her laboratory for six months.

"We truly don't know this part," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited commodity in Galápagos.

Methods to control the amphibians in the early 2000s were largely ineffective. Conservation officers tried capturing large numbers by hand and gradually increasing the salinity of ponds in vain.

Studies indicates spraying coffee – which is highly poisonous to frogs – or using electrocution could help, but these approaches aren't necessarily secure for other rare island organisms.

Lacking solutions to more of the fundamental issues about their biology and impact, culling the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she hopes the increasing use of environmental DNA techniques and genetic examination will assist her team make sense of the invader, funding for the project has been difficult to obtain.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to manage."